Cannot sign in to free teams anymore

[teacherphil]

When I initially started using microsoft teams free it was with a friend who has a business. He added me to a team and everything was fine. He then removed himself from the team and I continued using it, adding onenote notebooks etc. I noticed that when I logged into the desktop client that it was redirecting me to his microsoft teams each time. I rang him and asked him to remove me from his teams, no I can't access teams at all. I get the error AADSTS50020 and some rubbish about azure clients etc.

I just want to be able to have my own free teams that I login with my personal email. Any ideas. 

Phil

[#2]

@teacherphil Are you able to change Organizations even though the Teams client is having errors? There would be a drop down box near your account initials or picture in the upper right corner. I've attached a screenshot to help locate it.

[#3]

I am now back into teams after contacting my friend and he added me again. I cannot change orgs. There is no option in the drop down box. He has the org option, but not me.